Rename templates to <current-name>.hubl.html

[johnsfuller]

Problem

In new cms-react templates, the general consensus on template naming conventions for hubl templates seems to be template-name.hubl.html

Proposal

Let's rename all files in the /templates directory to match the hubl naming convention

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Checklist

• I have read the CONTRIBUTING document.
• I have checked the issue tracker to make sure there isn’t already an open issue.